IMPROVED HYDRAULIC BRAKE ARRANGEMENT FOR OFF-ROAD VEHICLE

Abstract

 Hydraulic brake arrangement (1) for controlling rear and/or front brakes (3, 4) of an off-road vehicle, comprising a source (2) of fluid in pressure, a power stage valve (5) fluidly interposed between source (2) and rear and/or front brakes (3, 4) and a pilot stage (6), pilot stage (6) being configured to provide a first and a second hydraulic load signals to control power stage valve (5) to allows fluid from source (2) to flow towards rear and/or front brakes (3, 4), power stage valve (5) comprising a gain valve (26), a logic valve (33) and a plurality of security valves (45a, 45b, 38), fluidically in series one with the other in a configuration to allow fail-safe and hydraulically-controlled actuation of rear and/or front brakes (3, 4).

Description

TECHNICAL FIELD

[0001] The present invention concerns a hydraulic brake arrangement, in particular a hydraulic brake arrangement for an off-road vehicle, such as an agricultural vehicle.

BACKGROUND OF THE INVENTION

[0002] Off-road vehicles such as agricultural vehicles use hydraulic brake arrangement for braking the vehicle because of the huge mass of the vehicle which has to be braked. However, existing hydraulic brake arrangements for off-road vehicles suffer of a plurality of drawbacks.

[0003] A first limit is given by master brake cylinders which has a defined, i.e. limited, volume which is delivered to brake valves by pressing brake pedal. This feature is a great limitation if the same master brake cylinders need to activate front brakes or if brakes change their dimensions, thereby requiring a bigger hydraulic flow for their operation.

[0004] A further limit is due by the fact that pressure imparted to brakes valve is proportional to the force applied to brake pedal of the master cylinder. Accordingly, if needed, the user has to impart a very high force on such pedal, thereby making the brake uncomfortable.

[0005] Furthermore, currently no fallback features are present in case of hydraulic failure on one side of the hydraulic circuit. Indeed, hydraulic fluid would flow into the lowest pressure side passing from balancing pressure conduit which is usually present between master brake cylinders.

[0006] According to the above, the need is felt to improve existing hydraulic brake arrangement to improve their operation, even if in case of hydraulic failure, and to improve comfort of the operator.

[0007] An aim of the present invention is to satisfy the above mentioned needs, in a cost-effective way.

SUMMARY OF THE INVENTION

[0008] The aforementioned aim is reached by a hydraulic brake arrangement as claimed in the appended set of claims.

BRIEF DESCRIPTION OF DRAWINGS

[0009] For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawings wherein:

• Figure 1 is a scheme of a hydraulic circuit according to the present invention;
• Figure 2 is a scheme of a hydraulic circuit of hydraulic circuit for balancing master brake cylinders according to the present invention; and
• Figure 3 is a schematic sectional view of a balancing valve which operates according to the scheme disclosed in figure 2.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Figure 1 discloses a hydraulic brake arrangement 1 according to the invention comprising a source 2 of fluid in pressure fluidly connected to left and right rear brakes 3a, 3b and front brakes 4, a power stage valve 5 which is fluidly interposed between source of fluid in pressure 2 and brakes 3a, 3b, 4 and a pilot stage 6 configured to control power stage valve 5.

[0011] In particular, power stage valve 5 advantageously comprises a first opening 5a fluidly connected to source 2 via a related conduit 8, a second opening 5b fluidly connected to a discharge 9 via a related conduit 11, a third and a fourth openings 5c, 5d respectively fluidly connected via respective conduits 12, 13 to pilot stage 6, a fifth and a sixth openings 5e, 5f respectively fluidly connected via respective conduits 15, 16 to left and right rear brakes 3a, 3b, a seventh opening 5g fluidly connected to front brake 4 via a related conduit 17 and a eight opening 5h fluidly connected to pump 18 via a related conduit 14.

[0012] Source 2 may comprise a pump 18 configured to supply fluid in pressure to power valve stage 5 via conduit 8 and at least an accumulator 19, fluidly connected to conduit 8 downstream with respect to pump 18, configured to supply fluid in pressure to power stage 5 via conduit 8 if pump 18 is not working/in fault.

[0013] According to such described configuration, source 2 is advantageously provided with a check valve 21 configured to allow passage of fluid only from pump 18 towards power stage thereby denying passage of fluid from accumulator 19 to pump 18, if accumulator 19 is activated.

[0014] Pilot stage 6 advantageously comprises a left and a right master cylinders 22a, 22b of known typology each provided with a brake pedal 23a, 23b. These latter, when pressed, are configured to impart a hydraulic pressure signal in conduits 12, 13 via master cylinders 22a, 22b.

[0015] Master cylinders 22a, 22b are furthermore connected by a pressure balance conduit 24 described in further detail hereinafter.

[0016] Power stage valve 5 is configured to receive a hydraulic signal from conduits 12, 13, proportional to the pressure received by master cylinders 22a, 22b in order to control the fluid coming for source 2 among brakes 3a, 3b and 4.

[0017] In particular, power stage valve 5 comprises a gain valve 26 fluidly interposed between conduit 8, 11 and 14 and configured, in function of the balance of two hydraulic signals acting on opposite sides of the spool of gain valve 26, to increase the pressure of fluid coming from conduit 8 towards a first intermediate output conduit 27 or to drain fluid in first intermediate output conduit 27 to conduit 14, which is fluidly connected as loading signal to pump 18.

[0018] Accordingly, gain valve 26 is a proportional hydraulic actuated valve having three ways and two-positions. First hydraulic signal acting on a first side valve 26 is taken by a conduit 28 on conduit 14 while a second hydraulic signal acting on the opposite side is taken by a conduit 29 fluidly connected to a shuttle valve 31 fluidly interposed between conduits 12 and 13. Second hydraulic signal is furthermore assisted by the force of an elastic element 32 acting against first hydraulic signal.

[0019] Power stage valve 5 comprises a logic valve 33 fluidly interposed between first intermediate output conduit 27 and a second, a third and a fourth intermediate conduits 34a, 34b, 35 configured, in function of the balance of two hydraulic signals acting on opposite sides of the spool of logic valve 33, to divide the fluid coming from first intermediate output conduit 27 towards second, a third and a fourth intermediate conduits 34a, 34b, 35.

[0020] Accordingly, logic valve 33 is a proportional hydraulic actuated valve having four ways and three positions. First hydraulic signal acting on a first side of valve 33 is taken by a conduit 36a derived by conduit 13 while a second hydraulic signal acting on the opposite side is taken by a conduit 36b derived by conduit 12. Both hydraulic signals are assisted by related springs 37a, 37b. In particular, in a first position wherein first hydraulic signal is greater than the second, fluid may flow only towards conduit 34a, in a second position, opposite with respect the first, fluid may flow only towards conduit 34b while in a third intermediate position fluid is divided between conduits 34a, 34b and 35.

[0021] Power stage valve 5 comprises a selection valve 38 fluidly interposed on conduit 35 between logic valve 33 and seventh opening 5g. Selection valve 38 is a two ways - two positions valve configured to assume a first position wherein there is free fluidic communication in conduit 35 and a second position wherein fluid may only flow from opening 5g towards logic valve 33 in function of two hydraulic signals acting on opposite sides of selection valve 38.

[0022] In particular, a first hydraulic signal is taking by a conduit 41 fluidly connected to output of valve 38 itself on conduit 35 and a second hydraulic signal is taken by a conduit 42 fluidly connected to conduit 29. Furthermore, first hydraulic signal is assisted by the force of an elastic element 43 acting on the same side of valve 38.

[0023] Power stage valve 5 further comprises a pair of security valves 45a, 45b fluidly interposed between fifth and sixth openings 5e, 5f and conduits 34a, 34b and configured, in function of a balance between respective hydraulic signals, to allow fluidic communication between conduits 34a, 34b towards openings 5e, 5f or between conduits 12 and 13 with these latter or no fluidic communication at all.

[0024] In particular, making reference for simplicity to security valve 45a, it is a three position - three ways valve wherein a first hydraulic signal acts on a first side of the spool of valve 45a and derived by a conduit 46a fluidly connected to conduit 13 and a second hydraulic signal is derived by a conduit 48a fluidly connected to conduit 34a and by a conduit 49a fluidly connected to output of valve 45a which both acts on the opposite side of this latter. Furthermore, second hydraulic signal is assisted by the force imparted by an elastic element 47a. In a mirrored way, valve 45b comprise the same elements, having the same reference number together with letter b in figure 1.

[0025] In a first position, wherein second signal is greater than first signal, valves 45a, 45b are positioned so that fluid may flow from logic valve 33 towards brakes 3a, 3b, while in a second opposite position, no fluid will pass. In an intermediate position fluid will pass from conduits 12, 13 towards brakes 3a, 3b.

[0026] Figure 2 discloses in greater detail the structure of balance pressure conduit 24 which can be fluidly interposed between master cylinders 22a, 22b. For simplifying, it is disclosed a simplified hydraulic brake arrangement 1' wherein output of master cylinders 22a, 22b is directly connected to right and left rear brakes 3a, 3b via conduits 3a', 3b'.

[0027] In particular balance pressure conduit 24 may be provided of a security balance device 50 configured to assume a first state into which fluid pass with a resistance from one to the other master cylinders 22a, 22 in order to balance a pressure difference between this latter and a second position into which fluid cannot pass between master cylinders. In particular, such condition is a safety condition because it may happens that one side of the hydraulic circuit faults and, according to known balance devices, pressurized fluid in pressurized side of the circuit will discharge from the fault side.

[0028] In particular, such security balance device 50 may comprise a pair of safety valves 51a, 51b, preferably in series one with respect to the other and each fluidly connected to the respective master cylinder 22a, 22b. Such safety valves 51a, 51b are maintained in open position by related springs 52a, 52b which defined a force which limit the difference of pressure between master cylinders 22a, 2b. If such force overcome such threshold, valves 51a, 51b move and avoid fluidic communication between master cylinders 22a, 22b.

[0029] For greater clarity interpretation am exemplarily physic embodiment of security balance device 50 is shown in figure 3.

[0030] According to the described embodiment, security balance device 50 comprise a spool 60 having a tubular shape around an axis A so that defining an inner volume 61. Spool 60 further comprises, housed inside volume 61 a pair of terminal caps 62a, 62b threaded to spool 60 so as to define respective openings 63a, 63b respectively fluidly connectable to pressure balance conduit 24, i.e. to master cylinders 22a, 22b, and to define respective shoulders 64a, 64b with respect to inner surface of spool 60 inside volume 61.

[0031] According to the above defined structure, security balance device 50 comprises a sliding element 65 housed inside volume 61 between caps 62a, 62b. Sliding element 65 comprises a main cylindrical portion 65a defining two extremities 65a', 65a" configured to cooperate at contact with shoulders 64a, 64b so as to close passage of fluid through respective openings 63a, 63b.

[0032] Sliding element 65 further comprises a relief portion 65b extending radially from cylindrical portion 65a and configured to cooperate at contact in tight manner with inner surface of spool 60 so that divides volume 61 into a firs portion 61a faced to cap 62a and a second portion 61b faced to cap 62b.

[0033] Security balance device 50 further comprises a pair of elastic elements 66a, 66b, e.g. coil springs, housed respectively in first and second portions 61a, 61b of volume 61 and comprising a first extremity cooperating with shoulders 64a, 64b and a second extremity cooperating with relief portion 65b. Stiffness of elastic elements 66a, 66b is set to be equal so that sliding element 65 is maintained in a substantially centered position inside volume 61 with respect to caps 62a, 62b.

[0034] Sliding element 65 is provided with a channel system 70 configured to allow fluidic communication between first and second portion 61a, 61b of volume 61 and, accordingly, between first and second openings 63a, 63b. According to the described arrangement, channel system 70 comprises a pair of radial conduits 71a, 71b passing through cylindrical portion 65a of sliding element 65 respectively in the portion of this latter placed inside first and second volume portions 61a, 61b. Channel system 70 further comprises an axial conduit 72, preferable coaxial to axis A, realized inside sliding element 65 and fluidly connecting radial conduits 71a, 71b.

[0035] The operation of the above described hydraulic brake arrangement 1 is the following.

[0036] Making reference to figure 1, fluid in pressure is always available upstream to gain valve 26 which is, in rest position, positioned so that fluid cannot flow to conduit 27.

[0037] In a normal operation of hydraulic brake arrangement 1, Supposing that driver presses both pedals 23a, 23b of master cylinders 22a, 22b to brake, respective signals on conduit 12, 13, proportional to such pressure input, will pass on conduit 29, thereby pushing spool of valve 26 so that it allows passage of fluid from conduit 8 towards conduit 27, further increasing its pressure of a preset ratio, e.g. 1 : 1, 5.

[0038] Then, fluid passes to conduit 27 and flows to logic valve 33. Here, according to the balance between signals taken from conduits 12 and 13, it divides, as said, flow of fluid among conduits 34a, 34b and 34. In the described situation, since both pedals are pressed (equally), valve is positioned to allows fluidic communication towards all the three aforementioned conduits.

[0039] Then, fluid will pass from one side to conduits 34a, 34b and then to security valves 45a, 45b which are placed by the balance of hydraulic signals taken on conduits 46a, 48a, 49a and 46b, 48b, 49b so that they allow passage of fluid towards conduits 15, 16 and thereby to rear brakes 3a, 3b.

[0040] Similarly, fluid pass to conduit 35 and, then to selection valve 38, which allows, according to balance between hydraulic signals 42 and 41 fluid to pass to front brake 4.

[0041] Supposing that a fault occurs in conduits 34a, 34b or upstream to logic valve 33 so that fluid pressure decreases, then force of hydraulic signal taken by conduits 46a, 46b will push valves 45a, 45b so that fluid of signals 12, 13 directly flows to conduits 15 and 16, i.e. controls brakes 3a, 3b.

[0042] Supposing that, further, a fault occurs in conduits 15, 16, hydraulic signal taken by conduits 46a, 46 will push valves 45a, 45b to avoid fluid passage towards brake 3a, 3b, i.e. to avoid fluid dispersion.

[0043] Similarly, supposing that a fault occurs in conduit 17, then hydraulic signal taken by conduit 42 will push valve 38 so that flow of fluid cannot pass from logic valve 33 towards front brakes 4, thereby avoiding fluid dispersion.

[0044] Making reference to figures 2 and 3, the operation of security balance device 50 is the following.

[0045] In a standard operation of hydraulic brake arrangement 1' , any pressure variation in left or right side of brake arrangement 1', e.g. due to master brake cylinders 22a, 22b or to impulse braking force or to an impulse on brake pedals 23a, 23b, will generate a flow of fluid passing from one of openings 63a, 63b via first and second volumes 61a, 61 through channel system 70, i.e. passing from right side to left side (or vice versa). The passage between channel system 70 and between terminal cylindrical portions 65a', 65a" and shoulders 64a, 64b generates respective narrowing which smoots/dampens passage of fluid between openings 63a, 63b.

[0046] Elastic elements 66a, 66b acts on sliding elements 65 if this latter moves for a greater pressure difference between openings 63a, 63b.

[0047] When a fault occurs in one between right and left side of hydraulic brake arrangement 1', pressure difference between openings 63a, 63b is so important that one of elastic elements 66a, 66b is pressed till reaching is minimum axial extension until closing fluid passage because of contact cooperation of terminal portions 65a', 65a" of cylindrical portions 65a and shoulders 64a, 64b.

[0048] In this way, fluid dispersion from safe side of hydraulic arrangement 1' towards the fault side through balance pressure conduit 24 is avoided.

[0049] In view of the foregoing, the advantages of a hydraulic brake arrangement 1 according to the invention are apparent.

[0050] The proposed layout is versatile, compact and allows braking with low pressure needed on brake pedals 23a, 24a while providing a great pressure fluid on brakes 3 and 4. Accordingly, comfort of the driver is increased.

[0051] Furthermore, the presence of security valves 38, 45a, 45b allows to preserve braking function also in case of hydraulic deficiencies/failures from upstream to this latter, allowing directly braking by master cylinders 22a, 22b.

[0052] Similarly, if problems arise downstream to security valves, i.e. brake hose is broken, they can isolate upstream conduits to prevent discharge of the circuit from the failed hose.

[0053] Furthermore, all valves are merely hydraulic actuated valves, accordingly there is no need for complex electronic actuation with related need of programmable control software.

[0054] Again, the use of a safety balancing valve 50 on balance conduit 24 allows at the same time to balance pressure difference between first and second master cylinders 22a, 22b.

[0055] The use of the proposed layout of spool 60 with sliding elements 65 allows a compact balance and safety function, thereby preventing discharge of hydraulic brake arrangement from pressurized side of the circuit to the failed one.

[0056] It is clear that modifications can be made to the described hydraulic brake arrangement 1 which do not extend beyond the scope of protection defined by the claims.

[0057] For example, it is clear that conduit topography and signals derivations may be changed according to design conditions.

[0058] Furthermore it is clear that gain, logic and safety valves may be realized thanks to equivalent valves maintaining the same claimed functions.

[0059] Again, safety balance device can be realized with a different layout and, similarly, spool 60 and sliding element 65.

Claims

1. Hydraulic brake arrangement (1) for controlling rear and/or front brakes (3, 4) of an off-road vehicle, said hydraulic brake arrangement (1) comprising a source (2) of fluid in pressure, a power stage valve (5) fluidly interposed between said source (2) and said rear and/or front brakes (3, 4) and a pilot stage (6), said pilot stage (6) being configured to provide a first and a second hydraulic load signals to control said power stage valve (5) to allows fluid from said source (2) to flow towards said rear and/or front brakes (3, 4), said power stage valve (5) comprising a gain valve (26), a logic valve (33) and a plurality of security valves (45a, 45b, 38),
said gain valve (26) being fluidly interposed between said source (2) and said logic valve (33) and being configured to assume at least a first position in which it allows passage of fluid to said logic valve (33) while increasing pressure value of the this latter and a second position into which fluid passage is prevented, in function of the greatest between said first and second hydraulic load signals;
said logic valve (33) being fluidly interposed between said gain valve (26) and said plurality of security valve (45a, 45b, 38) and being configured to subdivide the flow of fluid among at least one of said plurality of security valves (45a, 45b, 38) in function of said first and second hydraulic load signals;
said plurality of security valves (45a, 45b, 38) being fluidly interposed between said logic valve (33) and said rear and/or front brakes (3, 4) and being configured to allow passage of fluid from logic valve (33) to said rear and/or front brakes (3, 4) or to allow passage of said first and second hydraulic load signals or no passage of fluid towards said rear and/or front brakes (3, 4) in function of said first and second hydraulic load signals and at least one hydraulic signal taken from upstream or downstream with respect to said security valves (45a, 45b, 38).

2. Hydraulic brake arrangement according to claim 1, wherein said gain valve (26), said logic valve (33) and said plurality of security valves (45a, 45b, 38) are solely hydraulically controlled valves.

3. Hydraulic brake arrangement according to claim 1 or 2, wherein said gain valve (26) is a proportional valve.

4. Hydraulic brake arrangement according to any of claims 1 to 3, wherein said plurality of security valves (45a, 45b) comprises a three ways - three positions valve configured to assume a first position wherein no fluid may flow from said logic valve (33) to said rear brakes (3), a second position wherein fluid may flow from said logic valve (33) to said rear brakes (3) and a third position wherein fluid may flow from said first and second hydraulic signals may flow directly to said rear brakes (3), said positions are assumed in function of said first and second hydraulic signals against a sum of a hydraulic signal taken upstream to said security valves (45a, 45b) and a hydraulic signal taken downstream to said security valves (45a, 45b).

5. Hydraulic brake arrangement according to any of claims 1 to 4, wherein said plurality of security valves (38) comprises a two ways- two positions valve configured to assume a first position allowing fluidic communication between said logic valve (33) and said front brakes (4) and a second position allowing fluidic communication only from said logic valve (33) and said front brakes (4) in function of the greatest between said first and second hydraulic signals and at least a signal taken downstream with respect to said valve (38).

6. Hydraulic brake arrangement according to any of the preceding claims, wherein said source of fluid (2) comprises a pump (18) configured to supply fluid to said power stage valve (5).

7. Hydraulic brake arrangement according to claim 6, further comprising an accumulator (19) fluidly interposed in parallel between said pump (19) and said power stage valve (5).

8. Hydraulic brake arrangement according to any of the preceding claims, wherein said pilot stage (6) comprises a first and a second master cylinders (22a, 22b), said first and second master cylinders (22a, 22b) being configured to supply a first and a second hydraulic signals to said power stage valve (5) when a pressure is acting on this latter.

9. Hydraulic brake arrangement according to claim 8, wherein said pilot stage (6) comprises a balance pressure conduit (24) fluidly interposed between said first and a second master cylinders (22a, 22b), said pilot stage (6) fluidly comprising a safety balance device (50) interposed on said balance pressure conduit (24) and configured to allow fluidic communication between said first and a second master cylinders (22a, 22b) only below a predetermined pressure difference level between first and second master cylinders (22a, 22b).

10. Hydraulic brake arrangement according to claim 9, wherein said safety balance device (50) comprises two ways - two positions valves (51a, 51b) fluid in series one with respect to the one on said balance pressure conduit (24).

11. Hydraulic brake arrangement according to claim 10, wherein valves (51a, 51b) are fluidly actuated against a force of an elastic element (52a, 52b) by hydraulic signals taken upstream and downstream with respect to said valves (51a, 51b).

12. Hydraulic brake arrangement (1') for controlling rear and/or front brakes (3, 4) of an off-road vehicle, said hydraulic brake arrangement comprising a first and a second master cylinders (22a, 22b), said first and second master cylinders (22a, 22b) being configured to supply a first and a second hydraulic signals configured to control rear and/or front brakes (3, 4), said hydraulic brake arrangement (1') further comprising a balance pressure conduit (24) fluidly interposed between said first and a second master cylinders (22a, 22b), and a safety balance device (50) interposed on said balance pressure conduit (24) and configured to allow fluidic communication between said first and a second master cylinders (22a, 22b) only below a predetermined pressure difference level between first and second master cylinders (22a, 22b).

13. Hydraulic brake arrangement according to claim 12, wherein said safety balance device (50) comprises two ways - two positions valves (51a, 51b) fluid in series one with respect to the one on said balance pressure conduit (24).

14. Hydraulic brake arrangement according to claim 13, wherein valves (51a, 51b) are fluidly actuated against a force of an elastic element (52a, 52b) by hydraulic signals taken upstream and downstream with respect to said valves (51a, 51b).

15. Hydraulic brake arrangement according to any of claims 12 to 14, wherein said safety balance device (50) comprises a spool (60) defining an inner volume (61) and two openings (63a, 63b) fluidly communicating with said volume (61) and fluidly connectable to said first and a second master cylinders (22a, 22b), said safety balance device (50) comprising a sliding element (65) sliding in said volume (61) between said openings (63a, 63b) in function of a difference of pressure between these latter and dividing said volume (61) in a first portion (61a) communicating with said first opening (63a) and a second portion (61b) communicating with said second opening (63b), said sliding element (65) being configured to close one of said openings (63a, 63b) when driven by a pressure exceeding a predefined threshold of said difference pressure.

16. Hydraulic brake arrangement according to claim 15, wherein said safety device (60) comprises a pair of elastic elements (66a, 66b) housed inside said first and second portion (61a, 61b) and each configured to provide a force to said sliding element (65) so as to displace this latter with respect to said openings (63a, 63b) when driven by a pressure lower than a predefined threshold of said difference pressure.

17. Hydraulic brake arrangement according to claim 16, wherein said of elastic elements (66a, 66b) have the same stiffness.

18. Hydraulic brake arrangement according to any of claims 15 to 17, wherein said sliding element (65) divides said portions (61a, 61b) in tight manner and comprises a channel system (70) configured to allow passage of fluid between said portions (61a, 61b) through sliding elements (65) itself.

Drawing